The human body contains a wide variety of natural valves, such as, for example, heart valves, esophageal and stomach valves, intestinal valves, and valves within the lymphatic system. Natural valves can degenerate for a variety of reasons, such as disease, age, and the like. A malfunctioning valve fails to maintain the bodily fluid flow in a single direction with minimal pressure loss. An example of a malfunctioning valve is a heart valve that may be either stenotic, i.e., the leaflets of the valve do not open fully, or regurgitant, i.e., the leaflets of the valve do not close properly. It is desirable to restore valve function to regain the proper functioning of the organ with which the valve is associated. For example, proper valve function in the heart ensures that blood flow is maintained in a single direction through a valve with minimal pressure loss, so that blood circulation and pressure can be maintained. Similarly, proper esophageal valve function ensures that acidic gastric secretions do not irritate or permanently damage the esophageal lining.
Several percutaneous prosthetic valve systems have been described. One example described in Andersen, et. al. (U.S. Pat. No. 5,411,552) comprises an expandable stent and a collapsible valve which is mounted onto the stent prior to deployment. The collapsible valve may be a biological valve or it may be made of synthetic material. The Anderson prosthetic valve is delivered and deployed using a balloon catheter which balloon is used to expand the valve-stent prosthesis to its final size. See also, U.S. Pat. No. 6,168,614 (Andersen, et al.) entitled “Valve Prosthesis for Implantation in the Body” and U.S. Pat. No. 5,840,081 (Andersen, et al.) entitled “System and Method for Implanting Cardiac Valves.”
Spenser, et. al. (U.S. Pat. No. 6,893,460) describe another prosthetic valve device comprising a valve structure made of biological or synthetic material and a supporting structure, such as a stent. The Spenser prosthetic valve is a crimpable leafed-valve assembly consisting of a conduit having an inlet and an outlet, made of pliant material arranged to present collapsible walls at the outlet. The valve assembly is affixed to the support stent prior to deployment. The complete valve device is deployed at a target location within the body duct using a deploying means, such as a balloon catheter or a similar device.
Percutaneous implantation of prosthetic valves is safer, cheaper, and provides shorter patient recovery time than standard surgical procedures. However, current artificial percutaneous prosthetic valves have the disadvantage of being extremely bulky, even when compressed for delivery. The problem with this bulkiness is that it requires the delivery catheter to have a rather large diameter. Large catheters generally are not suitable for percutaneous procedures and require cut-down procedures and a surgeon and/or sophisticated and difficult puncture-closure techniques. The bulkiness and large diameter of current valve devices and delivery systems combined with the anatomy through which the devices must be delivered also can make delivery into the lumen problematic from the point of view of success rate, accuracy of deployment, and risk of complications. Specifically, delivery complications may arise due to the shape of the lumen, for example, the significant natural curve of the aortic arch and/or a tortuous iliac/femoral artery through which the catheter is introduced. Further, a catheter of such diameter tends to be less flexible than a smaller diameter catheter, especially when loaded with a bulky, inflexible device, and manipulating such a loaded catheter through a narrow vessel and in particular a curved vessel substantially raises the potential for damage to that vessel wall.
Accurate placement of current percutaneous valve devices relative to the existing native anatomy is often problematic, particularly in the case of aortic valve replacements. A prosthetic valve that is placed too distally (i.e., toward the aorta) can occlude or impede flow into the orifices of the coronary arteries. For example, depending on the position of the coronary ostia, either the skirt of the prosthetic valve or large native valve leaflets pressed down against the aorta wall may physically or functionally obstruct the orifices and impede coronary arterial flow. See, e.g., Piazza, N., et al., “Anatomy of the Aortic Valvar Complex and Its Implications for Transcatheter Implantation of the Aortic Valve,” CIRCULATION CARDIOVASCULAR INTERVENTIONS, 1:74-81 (2008); Webb, J G, et al., “Percutaneous aortic valve implantation retrograde from the femoral artery,” CIRCULATION, 113:842-850 (2006). This obstruction may be either physical or it may be functional, i.e. the orifices of the coronary arteries are physically patent, but due to alterations in flow patterns produced by the prosthetic valve, flow into the coronary arteries is partially compromised. A prosthetic valve that is placed too proximally (i.e., toward the ventricular outflow tracts of the left ventricle) can interfere with the anterior leaflet of the Mitral valve, the atrioventricular node, or the bundle of His (conduction tissues). Approximately thirty percent of patients receiving prosthetic valves percutaneously require pacemakers, because the valve is placed with the ventricular end too close to or on top of the left bundle branch, putting pressure on the electrical conduction apparatus. See, e.g., Piazza, N., et al., “Early and persistent intraventricular conduction abnormalities and requirements for pacemaking following percutaneous replacement of the aortic valve,” JACC CARDIOVASCULAR INTERVENTIONS, 1:310-316 (2008); Piazza, N., et al., “Anatomy of the Aortic Valvar Complex and Its Implications for Transcatheter Implantation of the Aortic Valve,” CIRCULATION CARDIOVASCULAR INTERVENTIONS, 1:74-81 (2008).
Therefore, a need exists to facilitate the delivery of artificial valves and also to increase the safety of the procedure. A valve device having a smaller delivery diameter than pre-assembled percutaneous valve devices and that can be delivered through vessel without incurring further damage to the wall of the body lumen is highly desirable.